Electronic navigation and information systems have been implemented in automotive vehicles. These systems alleviate the driver or the passengers of an automotive vehicle from the task of finding the best route to a destination. Such systems are particularly useful in regions unfamiliar to the driver in that it avoids the tedious tasks of map interpretation.
These systems have further been adapted to display the current position and traveling direction of the automotive vehicle in correlation with a map image overlapped on a display screen of a cathode ray tube (CRT) display unit located adjacent the driver's seat of the vehicle so as to further assist the driver in navigation tasks.
In order for such a system to provide the aforementioned navigation services, the system must be oriented to the actual position of the automotive vehicle relative to a road map. The actual position of an automotive vehicle may be determined by using systems such as: (a) the global positioning system (GPS); (b) the LORAN navigation system; (c) an inertia navigation system, e.g., the dead-reckoning system; or (d) a radar-like service such as ranging.
For example, the global positioning system (GPS) determines the position of an automotive vehicle in a global geometrical region through the method of triangularization. Typically, a global positioning system includes a receiver for receiving radio waves transmitted from three or more GPS satellites. The global positioning system determines the position of a reception point where the receivers have received the radio waves, based on quasi-distance data between the GPS satellites and the reception point, including a time offset of the receiver, and positional data of the GPS satellites.
Most modern GPS-based vehicle navigation systems can be divided into two categories: 1) map approach and 2) direction approach. A map approach navigation system displays a street map stored on a local storage device and the position of the vehicle on the map. If the vehicle is moving the map approach system will show the trace of the moving vehicle. As shown in FIG. 1a, the map shows the current position of the vehicle with a circle and an arrow 10 indicating the moving direction. The trailing circles show the trace of the moving vehicle.
The map approach is suited for people who like to see a bird's view of where they are. The map approach can also show the surrounding environment of the current position. The drawbacks of the map approach are: 1) the navigation direction is harder to understand; 2) the map is too complicated for some people; 3) the turn direction (left, right) depends on the moving direction of the vehicle which is confusing when the display shows the vehicle moving downward, e.g., as shown in FIG. 1b, the conventional right-turn arrow 11 looks like a left-turn arrow 12 when it moves downward; and 4) prior art maps display too much detail not relevant to the current driving situation.
A direction approach navigation system uses a simple display and/or audio messages to give driver directions according to the planned route identified by the system for the driver. For example, as shown in FIG. 2a, the system notifies the driver to turn right with arrow 14 at a next intersection which is 0.03 miles away.
Systems using the direction approach give the driver a prompt of what to do next. Drawbacks of this approach include: 1) typically the driver knows nothing about the surrounding environment; and 2) sometimes direction is hard to specify in an easily understood manner, e.g., in a complicated intersection as shown in FIG. 2b.
Furthermore, since these systems solely use local storage devices such as CD-ROM or magnetic hard disks to store the mapping and directional information, up-to-last-minute information is usually not available. This is especially important with respect to road changes, i.e., construction and or traffic conditions.